In a competitive examination, the average marks obtained was $45 .$ It was later discovered that there was some error in computerization and the marks of $90$ candidates had to be changed from $80$ to $50$ , and the average came down to $40$ marks. The total number of candidates appeared in the examination is 

  • A

    $520$

  • B

    $550$

  • C

    $540$

  • D

    $525$

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